All OPC communication is based on Microsoft COM (Component Object Model) technology. OPC uses DCOM (Distributed Component Object Model) technology for remote communication, so you must properly configure DCOM permissions to achieve successful communication between OPC components. Below are links to some whitepapers which will guide you through the the process of setting DCOM to enable all communication. This is preferable for testing/diagnostic purposes. DCOM permissions must be set appropriately for all OPC communications including OPCEnum. Please note, you must stop and restart any running applications in order for their specific DCOM modifications to take effect.
For more specific DCOM problems, use the search or contact support.